<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <div id="app">
    <p>{{ username }}</p>
    <p>{{ age >= 18 ? '成年' : '未成年' }}</p>
    <p>{{ friend.username }}是{{ age >= 18 ? '成年':'未成年'}}</p>
  </div>

  <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
  <script>
    const app = new Vue({
      el:'#app',
      data:{
        username:'zhangsan',
        age:18,
        friend:{
          username:'lisi',
          age:17
        }
      }
    })
  </script>

</body>

</html>